Humidifier

ABSTRACT

A humidifier includes a heating element including a porous structure of electrically resistive and thermally conductive material configured to substantially vaporise liquid that is passed through the porous structure. The porous structure has a liquid inlet and a vapour outlet. The humidifier further includes an outer housing surrounding at least a portion of the porous structure for containing the liquid and vapour within the porous structure. The porous structure includes a first electrical connector and a second electrical connector, the first and second connectors being configured for receiving electrical power and applying a voltage across the porous structure to generate heat.

This application is the U.S. national phase of International ApplicationNo. PCT/AU2012/000056 filed 24 Jan. 2012 which designated the U.S. andclaims priority to AU 2011900214 filed 24 Jan. 2011, and AU 2011901960filed 20 May 2011, the entire contents of each of which are herebyincorporated by reference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Australian Provisional Applications2011900214 and 2011901960, filed Jan. 24, 2011 and May 20, 2011,respectively, the entire contents of each being incorporated herein byreference.

FIELD OF THE TECHNOLOGY

The present technology relates to a humidifier and method for use inpatient ventilation, e.g., for treatment of Sleep Disordered Breathing(SDB) with Continuous Positive Airway Pressure (CPAP) or Non-InvasivePositive Pressure Ventilation (NIPPV), or treatment of other respiratorydisorders.

BACKGROUND OF THE TECHNOLOGY

CPAP treatment of SDB involves the delivery of a pressurised breathablegas, usually air, to a patient's airways using a conduit and mask. Gaspressures employed for CPAP typically range from 4 cm H₂O to 28 cm H₂O,at flow rates of up to 180 L/min (measured at the mask), depending onpatient requirements. The pressurised gas acts as a pneumatic splint forthe patient's airway, preventing airway collapse, especially during theinspiratory phase of respiration.

CPAP apparatus comprises a flow generator or blower for supplyingpressurised respiratory gas, such as air, to the patient via an airdelivery tube leading to a patient interface, such as a nasal ororonasal mask, or nasal cushion or nasal pillows arrangement.

CPAP machines are known which incorporate humidifying devices, eitherseparately from the flow generator or integrated therewith. An exampleof a flow generator/humidifier unit is the ResMed® S9 with H5ihumidifier sold by the present Applicant. The volume of such humidifiersis relatively large due to the requirement of a large surface area toheat the water supply, for example an approximate volume of 1680000 mm³(1,680 ml).

Humidification of the air supply is typically carried out by passing theair exiting the flow generator over the surface of a body of water in aheated water reservoir. However, such humidifiers are cumbersome and maybe prone to spillage, and are relatively slow to activate and to adjusthumidification level.

SUMMARY OF THE TECHNOLOGY

One aspect of the present technology relates to a humidifier. Thepresent technology also relates to a method which is suitable forhumidification of respiratory gases for patient treatment, e.g. ofrespiratory disorders. The humidification apparatus and method areconfigured to provide a rapid vaporisation of liquid for supply to therespiratory gases.

Another aspect of the present technology relates to a humidifier havinga small volume of liquid for vaporisation for supply to respiratorygases for patient treatment. In certain examples the volume of thehumidifier is between approximately 19000 mm³ (19 ml) and 190000 mm³(190 ml). Thus, the humidifier may be 20%, such as approximately 1-12%,smaller than current humidifiers by volume.

A further aspect of the present technology relates to a humidifier thatvaporises water at a slow rate, for example 0-10 ml/min, preferably 0-6ml/min, more preferably 0-1.5 ml/min.

A further aspect of the present technology relates to a humidifier thatvaporises a small volume of water, for example 0-10 ml, preferably 0-6ml, more preferably 0-1.5 ml.

In certain examples the volume of water is controlled to control thehumidification level delivered by the humidifier. In some examples, thepower to vaporise the water is controlled to control the humidificationlevel delivered by the humidifier.

Yet another aspect of the present technology relates to a humidifiercomponent comprising a porous structure of thermally conductive materialconfigured to act as a heating element to substantially vaporise liquid,for example water that is passed therethrough. In certain examples, theporous structure is an electrically conductive material such as metalfoam, through which both electric current and water are passed so thatthe porous structure acts as a resistance heater to vaporise at leastpart of the water within it.

A still further aspect of the present technology relates to a humidifiercomprising: a water supply, an electrical power supply, and a porousstructure of thermally conductive material having a water inlet incommunication with the water supply and a vapour outlet in communicationwith a gas stream to be humidified, the porous structure being connectedto the electrical power supply such that the porous structure acts as aheater to vaporise water within the porous structure as it travelstowards the vapour outlet. In certain examples the humidifier is ahumidifier for respiratory gases.

Another aspect of the present technology relates to a humidifiercomprising a water supply, a means for supplying a volume of water, anda steam generator, wherein the supply means is configured to supply avolume of water from the water supply as required to the steamgenerator, the steam generator substantially converts the volume ofwater into steam and the steam is supplied into a respiratory gas flowpath for delivery to a patient. The steam generator may comprise aporous structure of thermally conductive material though which thesupply of water is passed through.

In certain examples, the porous structure comprises a body of open poremetal foam or other electrically resistive and/or thermally conductivematerial. A porous structure is to be considered any structure having aplurality of pores that allows fluid to pass therethrough. Example poresize may be from about 0.1 to 2 mm pore diameter, for example from about0.2 to 1.0 mm, and such as about 0.4 mm.

Example metals for the foam include super alloys such as chromiumalloys. Example chromium alloys include MCrAlX, where M is one or moreof Nickel (Ni), Cobalt (Co) or Iron (Fe) contributing at least about 50%by weight, Chromium (Cr) contributing between 8% and 35% by weight,Aluminium (Al) contributing greater than 0% but less than about 8% byweight, and X contributing less than about 25% by weight, with Xconsisting of zero or more other elements, including but not limited toMolybdenum (Mo), Rhenium (Re), Ruthenium (Ru), Titanium (Ti), Tantalum(Ta), Vanadium (V), Tungsten (W), Niobium (Nb), Zirconium (Zr), Boron(B), Carbon (C), Silicon (Si), Yttrium (Y) and Hafnium (Hf). Anotherexample chromium alloy is a nickel-chromium alloy or Inconel® alloys.Other suitable materials may include porous ceramic materials such assilicon carbide, titanium nitride, or carbon such as pyrolytic carbon.

According to still another aspect of the present technology, the porousstructured steam generator may comprise fibrous materials which areelectrically resistive and/or thermally conductive. The body of fibresmay preferably be bundled in groups forming tow-, twist-, knit-, braid-,felt-, woven fabric- or tape-structures. The bundled fibrous structurehaving a plurality of apertures, or pores, which allow fluid to passtherethrough. Examples of fibrous materials include carbon fibres havinga carbon content of greater than about 50% and having precursors of PolyAcrylic Nitrile (PAN), rayon or pitch. The carbon fibre diameters may beless than 20 microns, for example about 5 to 7 microns.

Still another aspect of the present technology relates to a humidifierthat includes a tube surrounding at least a portion of the porousstructure for containing water and water vapour within the porousstructure. The porous structure and the tube may each be elongate, and avapour outlet end of the porous structure may be exposed to the gasstream to be humidified through an open end of the tube. In one example,the vapour outlet end of the porous structure extends beyond thesurrounding tube.

A still further aspect of the present technology relates to a humidifieradapted for mounting within an air delivery tube, and the arrangementfurther includes a mounting structure for mounting the humidifier withinthe air delivery tube. The mounting structure may be adapted to spacethe humidifier from the internal walls of the air delivery tube. Themounting structure may support and locate the humidifier within acentral location within the air delivery tube. In certain examples themounting structure may include a coil structure, such as a “porcupine”coil structure, adapted to mount the humidifier substantially parallelto the longitudinal axis of the air delivery tube.

According to one example of the present technology, a humidifiercomprises a heating element including a porous structure of electricallyresistive and thermally conductive material configured to substantiallyvaporise liquid that is passed through the porous structure, the porousstructure having a liquid inlet and a vapour outlet; an outer tubesurrounding at least a portion of the porous structure for containingthe liquid and vapour within the porous structure; a first power leadconnected to the liquid inlet by a first electrical connector; and asecond power lead connected to the vapour outlet by a second electricalconnector, wherein the first power lead and the second power lead areconfigured to apply a voltage across the porous structure.

Another aspect of the present technology relates to a respiratory deviceand method comprising an air heater coil adapted to heat the air flow.Preferably the air heater coil is configured to cover substantially allor most of the air flow path. The air coil heater may be located in aflow generator, humidifier, patient interface, air delivery tube and/orat any connection point between such devices.

According to a further aspect of the present technology, an air heatercoil comprising a plurality of offset or overlapping loops or “petals”to form a rosette configuration structured to cover substantially all ormost of the cross-sectional area of an air flow path to ensure the airflow is in close proximity to at least part of the heating wires at somestage of its flow.

According to another example of the present technology, a respiratoryapparatus for delivering a flow of breathable gas to a patient comprisesa flow generator configured to generate the flow of breathable gas; anda humidifier according to the present technology.

Another aspect of some forms of the present technology relates to amethod of treating a respiratory disorder with humidified air. Anotheraspect of some forms of the present technology relates to a method ofhumidifying air. Another aspect of some forms of the present technologyrelates to a method of operating a humidifier component. Another aspectof some forms of the present technology relates to a method of operatinga humidifier.

Further aspects and examples of the present technology will be apparentfrom the following description, and the appended claims. Further aspectsare described below.

According to aspect 1, a humidifier comprises a heating elementincluding a porous structure of electrically resistive and thermallyconductive material configured to substantially vaporise liquid that ispassed through the porous structure, the porous structure having aliquid inlet and a vapour outlet; an outer tube surrounding at least aportion of the porous structure for containing the liquid and vapourwithin the porous structure; a first power lead connected to the liquidinlet by a first electrical connector; and a second power lead connectedto the vapour outlet by a second electrical connector, wherein the firstpower lead and the second power lead are configured to apply a voltageacross the porous structure.

2. A humidifier according to aspect 1, further comprising a connectorconfigured to deliver liquid from a supply of liquid to the liquidinlet.

3. A humidifier according to aspect 2, wherein the connector comprises aconnection spigot, and the humidifier further comprises a sealing tubeconfigured to form a sealed connection between the connection spigot andthe outer tube.

4. A humidifier according to aspect 2 or aspect 3, wherein the connectorcomprises a liquid inlet spigot configured to receive liquid from aliquid supply.

5. A humidifier according to aspect 4, further comprising a liquidsupply tube connected to the liquid inlet spigot.

6. A humidifier according to any one of aspects 2-5, wherein theconnector comprises a sealing connector configured to seal the firstpower lead passing through the connector to the liquid inlet.

7. A humidifier according to any one of aspects 1-6, wherein the firstelectrical connector is a crimp connector.

8. A humidifier according to any one of aspects 1-7, wherein the porousstructure and the outer tube are each elongate, and the vapour outlet ofthe porous structure is configured to be exposed to a flow of breathablegas to be humidified through an open end of the outer tube.

9. A humidifier according to aspect 8, wherein the vapour outlet of theporous structure extends beyond the surrounding tube.

10. A humidifier according to aspect 8 or aspect 9, wherein the secondelectrical connector is a crimp connector.

11. A humidifier according to any one of aspects 1-10, wherein theporous structure has a cylindrical shape.

12. A humidifier according to any one of aspects 1-10, wherein theporous structure has a tapered shape.

13. A humidifier according to aspect 12, wherein the porous structurehas a larger diameter at the vapour outlet than at the liquid inlet.

14. A humidifier according to any one of aspects 1-13, wherein theporous structure is formed of an open pore metal foam.

15. A humidifier according to aspect 14, wherein the metal comprises achromium alloy.

16. A humidifier according to aspect 15, wherein the chromium alloycomprises MCrAlX, where M is one or more of Nickel (Ni), Cobalt (Co) orIron (Fe) contributing at least 50% by weight, Chromium (Cr)contributing between about 8% and 35% by weight, Aluminium (Al)contributing greater than 0% but less than about 8% by weight, and Xcontributing less than about 25% by weight, with X including zero ormore other elements, including to Molybdenum (Mo), Rhenium (Re),Ruthenium (Ru), Titanium (Ti), Tantalum (Ta), Vanadium (V), Tungsten(W), Niobium (Nb), Zirconium (Zr), Boron (B), Carbon (C), Silicon (Si),Yttrium (Y) and Hafnium (Hf).

17. A humidifier according to any one of aspects 14-16, wherein themetal foam is formed by pyrolysis and/or metallisation of a polymer foamsuch as an open cell polyurethane foam.

18. A humidifier according to any one of aspects 14-17, wherein themetal foam has an open pore volume of 90% or greater, for example about95%.

19. A humidifier according to any one of aspects 14-18, wherein a poresize of the metal foam is about 0.1 to 2 mm, for example about 0.2 to 1mm, such as about 0.4 mm.

20. A humidifier according to any one of aspects 1-13, wherein theporous structure comprises a body of fibres.

21. A humidifier according to aspect 20, wherein the body of fibres isbundled in a form of tow filaments, twist, knit, braid, woven fabric ortape structures.

22. A humidifier according to aspect 20 or 21, wherein the body offibres comprises carbon fibres having a carbon content of greater thanabout 50%.

23. A humidifier according to aspect 22, wherein the carbon fibers haveprecursors of Poly Acyrlic Nitrile, rayon and/or pitch.

24. A humidifier according to aspect 22 or aspect 23, wherein the carbonfibers have a diameter of less than about 20 microns, for example about5 to 7 microns.

25. A humidifier according to any one of aspects 1-13, wherein theporous structure is formed of ceramic material such as silicon carbide,titanium nitride or pyrolytic carbon.

26. A humidifier according to any one of aspects 1-25, wherein theporous structure has a substantially uniform porosity.

27. A humidifier according to any one of aspects 1-25, wherein theporous structure has a varying porosity along its length and/ordiameter.

28. A humidifier according to any one of aspects 1-27, wherein theporous structure has a diameter of between about 1 to 5 mm, for exampleabout 2 mm.

29. A humidifier according to any one of aspects 1-28, wherein theporous structure has a length of between about 20 to 200 mm, for exampleabout 100 mm.

30. A humidifier according to any one of aspects 1-29, wherein theporous structure has a volume of between about 10 to 4000 mm³, forexample about 15 to 500 mm³, such as about 314 mm³.

31. A humidifier according to any one of aspects 1-30, wherein the outertube is formed of electrically and thermally insulating material.

32. A humidifier according to aspect 31, wherein the outer tube isformed of alumina or fused quartz.

33. A humidifier according to aspect 31, wherein the outer tube isformed of a polymer, such as heat shrink or silicone rubber.

34. A humidifier according to any one of aspects 1-33, furthercomprising an air delivery tube and a mounting structure for mountingthe humidifier within the air delivery tube.

35. A humidifier according to aspect 34, wherein, the mounting structureis adapted to space the humidifier from an internal wall of the airdelivery tube.

36. A humidifier according to aspect 34 or aspect 35, wherein, themounting structure includes a coil structure adapted to mount thehumidifier substantially parallel to the longitudinal axis of the airdelivery tube.

37. A humidifier according to aspect 15, wherein the coil structurecomprises a resistant heater configured to heat air flowing through theair delivery tube.

38. A humidifier according to any one of aspect 1-37, further comprisinga liquid supply configured to supply liquid to the liquid inlet.

39. A humidifier according to aspect 38, wherein the liquid supplycomprises a micro-pump or a piezo electric pump.

40. A humidifier according to aspect 38, wherein the liquid supplycomprises a gravity feed.

41. A humidifier according to any one of aspects 38-40, wherein theliquid supply is configured to deliver about 2-10 ml/min, for exampleabout 2-6 ml/min, such as about 4-5 ml/min of liquid.

42. A humidifier according to any one of aspects 38-41, wherein theliquid supply is configured to supply water.

43. A humidifier according to any one of aspects 1-42, furthercomprising a power supply configured to supply the voltage across theporous structure.

44. A humidifier according to aspect 43, further comprising a controllerconfigured to control the power supply.

45. A humidifier according to aspect 44, wherein the controller controlsthe power supply sot that vapour is delivered only during an inspiratoryphase of a patient's breathing cycle.

46. A respiratory apparatus for delivering a flow of breathable gas to apatient, comprising:

a flow generator configured to generate the flow of breathable gas; and

a humidifier according to any one of aspects 1-45 configured to humidifythe flow of breathable gas.

47. A respiratory apparatus according to aspect 46, wherein the flowgenerator is configured to generate the flow of breathable gas at apressure of about 4 to 28 cm H₂O.

48. A respiratory apparatus according to aspect 46 or aspect 47, whereinthe flow generator is configured to generate a flow of breathable gas ofbetween about 100 to 180 L/min.

49. A respiratory apparatus according to any one of aspects 46-48,further comprising a least one sensor configured to detect a temperatureof ambient gas entering the flow generator, a relative humidity of theambient gas, an absolute humidity of the ambient gas, a temperature ofthe flow of breathable gas, a temperature of the humidified flow ofbreathable gas, a relative humidity of the humidified flow of breathablegas, an absolute humidity of the flow of breathable gas, a pressure ofthe flow of breathable gas, and a rate of the flow of breathable gas.

50. A respiratory apparatus according to aspect 49, further comprising acontroller configured to receive a signal from the at least one sensorand configured to control the humidifier to provide the humidified flowof breathable gas at a predetermined temperature and a predeterminedrelative humidity.

51. A respiratory apparatus according to aspect 50, wherein thecontroller of the respiratory apparatus is configured to control theflow generator and the power supply of the humidifier.

52. A respiratory apparatus according to any one of aspects 46-51,wherein the humidifier is disposed in a delivery tube between the flowgenerator and a patient interface configured to seal with the patient'sairways.

53. A respiratory apparatus according to any one of aspects 46-51,wherein the humidifier is disposed in a delivery tube between the flowgenerator and a patient interface configured to seal with the patient'sairways.

54. A humidifier comprises: a porous structure of thermally conductivematerial configured to act as a heating element to substantiallyvaporise liquid that is passed therethrough.

55. A humidifier according to aspect 54, wherein the porous structureacts as a resistance heater to vaporise at least part of the liquidwithin it.

56. A humidifier according to aspect 54 or aspect 55, wherein the porousstructure is formed of electrically resistive material.

57. A humidifier comprises an electrical power supply; and a porousstructure of thermally conductive material having a liquid inlet adaptedfor communication with a liquid supply and a vapour outlet incommunication with a gas stream to be humidified, the porous structurebeing connected to the electrical power supply such that the porousstructure acts as a heater to vaporise liquid within the porousstructure as it travels towards the vapour outlet.

58. A humidifier according to any one of aspects 54-57, wherein thehumidifier is a humidifier for respiratory gases.

59. A humidifier according to any one of aspects 54-58, wherein theporous structure comprises a body of open pore metal foam or a body offibres bundled in a form of tow filaments, twist, knit, braid wovenfabric or tape structures.

61. A humidifier according to aspect 59 or 60, wherein the body offibres comprises carbon fibres.

62. A humidifier according to any one of aspects 53-61, wherein thehumidifier further includes a tube surrounding at least a portion of theporous structure for containing liquid and vapour within the porousstructure.

63, A humidifier according to aspect 62, wherein the porous structureand the tube are each elongate, and a vapour outlet of the porousstructure is exposed to a gas stream to be humidified through an openend of the tube.

64. A humidifier according to aspect 62 or aspect 63, wherein the vapouroutlet of the porous structure extends beyond the surrounding tube.

65. A humidifier according to any one of aspects 53-64, wherein thehumidifier is adapted for mounting within an air delivery tube, and thearrangement further includes a mounting structure for mounting thehumidifier within the air delivery tube.

66. A humidifier according to aspect 65, wherein the mounting structureis adapted to space the humidifier from an internal wall of the airdelivery tube.

67. A humidifier according to aspect 65 or aspect 66, wherein themounting structure includes a coil structure adapted to mount thehumidifier substantially parallel to the longitudinal axis of the airdelivery tube.

68. A humidifier according to aspect 67, wherein the coil structure isfurther adapted to act as a resistant heater to heat air flowing throughthe air delivery tube.

69. A humidifier comprising: a supply means; and a steam generator,wherein the supply means is configured to supply a volume of water froma water supply as required to the steam generator, the steam generatorsubstantially converts the volume of water into steam and the steam issupplied into a respiratory gas flow path for delivery to a patient.

70. A humidifier according to aspect 69, wherein the steam generatorcomprises a porous structure of thermally conductive material throughwhich the supply of water is passed through.

71. A humidifier according to aspect 69, wherein the steam generatorcomprises a fibrous structure of thermally conductive material throughwhich the supply of water is passed through.

72. A humidifier according to aspect 71, wherein the fibrous structurecomprises bundled carbon fibre.

73. A humidifier according to any one of aspects 69-72, wherein therespiratory airflow is preheated.

74. A humidifier according to any one of aspects 69-73, wherein thesupply means is a pump configured to pump a volume of water to the steamgenerator.

75. A humidifier according to any one of aspects 69-74, wherein thesteam is delivered only during an inspiratory phase of the patient'sbreathing cycle.

76. A method of humidifying a flow of breathable gas, comprising:feeding liquid to an inlet of a porous structure of thermallyconductive, electrically resistive material; passing electric currentthrough the porous structure to vaporise the liquid; and exposing anoutlet of the porous structure to the flow of breathable gas to humidifythe flow of breathable gas.

77. A method according to aspect 76, further comprising: sealing theinlet of the porous structure from the flow of breathable gas.

78. A method according to aspect 76 or aspect 77, wherein feeding theliquid comprises pumping the liquid.

79. A method according to aspect 76 or aspect 77, wherein feeding theliquid comprises feeding the liquid by gravity.

80. A method according to any one of aspects 76-79, further comprising:determining at least one of an ambient temperature of gas used to formthe flow of breathable gas, a relative humidity of the gas used to formthe flow of breathable gas, an absolute humidity of the gas used to formthe flow of breathable gas, a pressure of the flow of breathable gas,and/or an amount of the flow of breathable gas; and controlling at leastone of the electric current, the feeding of the liquid to the inlet ofthe porous structure, and/or the volume of the flow of breathable gas toprovide at least one of a predetermined relative humidity, absolutehumidity, and/or temperature to the humidified flow of breathable gas.

81. A method according to any one of aspects 76-80, further comprising:heating the flow of breathable gas prior to exposing the flow ofbreathable gas to the outlet of the porous structure.

82. A method according to any one of aspects 76-81, wherein feeding theliquid to the inlet of a porous structure comprises feeding about 2-10ml/min, for example about 2-6 ml/min, such as about 4-5 ml/min ofliquid.

83. A method according to any one of aspects 76-82, wherein passing theelectric current through the porous structure comprises applying avoltage between about 12 V to 24 V to the porous structure.

84. A method according to any one of aspects 76-83, wherein exposing theoutlet of the porous structure to the flow of breathable gas comprisesexposing the outlet to a flow of breathable gas of between about 100 to180 L/min.

85. A method according to any one of aspects 76-84, wherein exposing theoutlet of the porous structure to the flow of breathable gas comprisesexposing the outlet to a flow of breathable gas at a pressure of betweenabout 4 cm H₂O to 28 cm H₂O.

86. An air heater coil adapted to heat an airflow within a respiratorydevice comprising a plurality of loops or petal, each loop or petalarranged to overlap an adjacent loop or petal to form a rosetteconfiguration adapted to cover substantially all or most of across-sectional area of an air flow path within the respiratory device.

87. An air heater according to aspect 86, wherein the respiratory deviceincludes one or more of the following components: a flow generator, ahumidifier, an air delivery tube, a patient interface and/or a connectorcoupled between such components, and the air heater is located in atleast one of the components.

88. An air heater according to any one of aspects 86-87, wherein theplurality of loops or petals are formed of resistive wire.

89. A method of heating the air flow within a respiratory devicecomprising: inserting the air heater according to any one of aspects86-88 into a component of the respiratory device and energising the airheater to heat the air heater to a desired temperature.

90. A method of controlling a humidifier to deliver a predeterminedlevel of humidity supplied to a patient interface, the method comprisingthe steps of determining the ambient absolute humidity; calculating arequired amount of liquid to be added to a flow of breathable gas;calculating an amount of energy required to vapourise the requiredamount of liquid; controlling a water supply unit to deliver therequired amount of liquid to a porous heating element; and energisingthe porous heating element with the amount of energy to vapourise therequired amount of liquid to deliver the required amount of liquid tothe flow of breathable gas.

91. A method of treating a respiratory disorder of a patient with apredetermined level of humidity comprising the steps of: providing asupply of air or breathable gas to the patient; determining an airflowrate of respiratory gas to the patient; determining a volume ofwater required to humidify the supply of air or breathable gas to thepredetermined level of humidity; determining the amount of energyrequired to deliver the required predetermined level of humidity;determining a phase of a respiratory cycle of the patient; heating thevolume of water to produce a volume of steam; and delivering the volumeof steam to the supply of air or breathable gas to the patient during aportion of the respiratory cycle of the patient.

92. The method of aspect 91 wherein the portion of the respiratory cycleof the patient is the inspiratory phase of the respiratory cycle of thepatient.

BRIEF DESCRIPTION OF THE DRAWINGS

Further examples of the present technology will now be described withreference to the accompanying drawings, in which:

FIGS. 1a to 1c are schematics of examples of a respiratory apparatusincorporating a humidifier according to the present technology;

FIG. 2a is a schematic perspective view of an example of a humidifierassembly according to one aspect of the present technology;

FIG. 2b is a schematic perspective view of another example of ahumidifier assembly according to an aspect of the present technology;

FIG. 3a is a photograph of an example metal foam material according toan aspect of the present technology;

FIG. 3b is a schematic view of an example bundled fibre materialaccording to an aspect of the present technology;

FIG. 4 is a longitudinal cross section showing the mounting of thehumidifier within the air delivery tube of a respiratory apparatusaccording to an aspect of the present technology;

FIG. 5 is an isometric view of the mounting structure of FIG. 4;

FIG. 6a is an isometric view of the mounting structure of FIGS. 4 and 5;

FIG. 6b is an end view of the mounting structure of FIG. 6 a;

FIG. 6c is a side view of the mounting structure of FIG. 6 a;

FIG. 6d is an illustration of dimensions of the coils of the mountingstructure of FIGS. 6a -6 c;

FIG. 6e is a side view of a mounting structure according to anotherexample of the present technology;

FIG. 7 is a view of a humidifier according to another aspect of thepresent technology;

FIG. 8 is a view of a mounting structure;

FIG. 9 is a view of another mounting structure;

FIG. 10 is a flow chart of a mode of operation of a humidifier accordingto an example of the present technology; and

FIG. 11 is a flow chart of a mode of operation of a humidifier accordingto another example of the present technology.

FIG. 12 is a chart showing empirical values of power required tovaporize an input water flow.

DETAILED DESCRIPTION

In this specification, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise”, “comprised” and “comprises” where they appear.

FIG. 1a is a schematic view of a respiratory apparatus including ahumidifier according to an example of the present technology. Theapparatus comprises a flow generator 10 for generating a supply of airunder positive pressure, a humidifier (or humidifier assembly) 12 forincreasing humidity of the gas from the flow generator, a patientinterface 14 such as a nasal or oronasal mask or nasal cushion or nasalpillows interface, interconnected by air delivery tubes 16 a, 16 b.Alternatively, the humidifier 12 may be configured to couple directly toan outlet of the flow generator 10 such that interconnecting deliverytube 16 a is not required (see FIG. 1b ), for example as in the ResMedS9™ PAP system. Furthermore, as illustrated in FIG. 1c and discussed inmore detail below, the humidifier 12 may be incorporated within theinterconnecting tube 16 b. In this arrangement a water supply (or watertub) 12 a having a water supply tube 12 b is required to provide asource of water (a supply of liquid) to the humidifier 12 located withinthe air delivery tube 16 b. The tubes 16 a, 16 b may have an internaldiameter of, for example, about 10 mm to 22 mm, such as about 15 mm to22 mm, for example about 12 mm, 13 mm, 14 mm, 15 mm, 19 mm. It should beappreciated that other diameters are possible.

The flow generator 10 may also include a controller 18 for receivinginput from a control interface (not shown) of the flow generator andsignal/s from one or more sensors 20 a, 20 b, 20 c, for controllingoperation of the flow generator 10 and humidifier 12. The sensors 20 a,20 b, 20 c may be one or more of temperature, pressure, relativehumidity, absolute humidity and/or flow sensors, for detecting, forexample, a property of ambient, unhumidified flow, and humidified flow.A sensor may determine a temperature of ambient air. The sensors 20 a,20 b, 20 c may be located remotely such as in the humidifier 12 and/orpatient interface 14 as indicated in FIG. 1a . Alternatively asindicated in FIG. 1 b the sensors 20 a, 20 b, 20 c may be located withinthe flow generator 10 and/or humidifier 12. It should be appreciatedthat the number and location of sensors 20 a, 20 b, 20 c may vary withthe different respiratory apparatus arrangements and that the sensors 20a, 20 b, 20 c may be provided in the flow generator 10 and/or thehumidifier 12 and/or the patient interface 14. It should also beappreciated that more sensors than those shown in FIGS. 1a to 1c mayalso be provided.

FIG. 2a illustrates a humidifier assembly according to an example of thepresent technology, including hidden detail shown in broken lines.

The humidifier assembly 12 includes a generally porous structure 24 of athermally conductive and electrically resistive porous material that isencased by an outer housing, for example a tube 26 which closelysurrounds the porous structure 24. As illustrated the porous structure24 may have a cylindrical shape; however other shapes may be utilised.One end 27 of the porous structure 24 may be a vapour outlet and mayextend beyond the open end of outer tube 26, as shown in FIG. 2 a.

A connector fitting 28 has a liquid (e.g. water) inlet 30, such as inthe form of a spigot, to form a liquid inlet spigot, for connection to aliquid supply tube 32 leading from a liquid/water supply (not shown).Water may be provided to the water supply tube using a supply (notshown), such as a pump or by gravity feed or other known watertransporting means, and a sealing tube connection spigot 34 forconnection of a sealing tube 36 which forms a sealed connection betweenthe connector fitting 28 and the outer tube 26. The connector fitting 28may include a three-way or multi-way connector for example a Y or Tshaped connector. An internal passageway within the connector allowswater flow from the water inlet spigot 30 to spigot 34, then through thesealing tube 36 and through the porous structure 24.

The connector fitting 28 further includes a sealing connector 35 forconnection of an electrically conducting wire 39 to the humidifier. Theconducting wire 39 has a first end 39 a that extends from an end of thehumidifier to connect to a power supply and a second end 39 b that isconnected to the porous structure 24 within the outer tube 26. Thesealing connector 35 is sealed to the conductor wire 39 passingco-axially with the sealing tube connection spigot 34, the second end 39b of the conductor wire 39 in turn being connected to an end 31 of theporous structure 24 located within the outer tube 26 by a connectionwith the first electrical connector 33, for example a crimp connection.

At the other, exposed, end 27 of the porous structure 24 is a connectionwith a second electrical connector 37, such as a crimp connector, forconnection of a power lead 38. The power lead 38 with the conductingwire 39 applies a voltage across the porous structure 24 to operate as aresistance heater. The applied voltage may be low voltage DC, such asabout 12V or 24V DC, e.g., taken from the flow generator power supply.Alternatively a separate power supply may be utilised. It should beappreciated that AC voltage may be used.

The porous structure 24 is composed of a thermally conductive, open porematerial which allows passage of water and/or water vapour therethrough.The porous material has an open pore area which is sufficiently porousto allow water to flow through the material, such as pumped through orgravity feed through, from the inlet to the outlet without requiringexcessive pressure. A detail view showing an example of the porousmaterial of the porous structure 24 is illustrated in FIGS. 3a and 3 b.

Example materials for the porous structure 24 may include porous metalor ceramic materials (e.g. silicon carbide or titanium nitride) having athermally conductive and resistivity suitable for use as a resistanceheater for the water contained within the pores of the material.Materials such as metal, resistive ceramic or carbon foams or fibres maybe suitable.

Example materials for the porous structure are metal foams such as thoseavailable from Recemat International BV of the Netherlands.Nickel-chromium aluminium or Inconel® metal foams have been found to besuitable. Other example metals for the foam include super alloys such aschromium alloys. Example chromium alloys include MCrAlX, where M is oneor more of Nickel (Ni), Cobalt (Co) or Iron (Fe) contributing at leastabout 50% by weight, Chromium (Cr) contributing between about 8% and 35%by weight, Aluminium (Al) contributing greater than 0% but less thanabout 8% by weight, and X contributing less than about 25% by weight,with X consisting of zero or more other elements, including but notlimited to Molybdenum (Mo), Rhenium (Re), Ruthenium (Ru), Titanium (Ti),Tantalum (Ta), Vanadium (V), Tungsten (W), Niobium (Nb), Zirconium (Zr),Boron (B), Carbon (C), Silicon (Si), Yttrium (Y) and Hafnium (Hf).Another example chromium alloy is a nickel-chromium alloy or Inconel®alloys. Other suitable materials may include porous ceramic materialssuch as silicon carbide, titanium nitride, or carbon such as pyrolyticcarbon. Other porous metals of sufficient strength, corrosion andleaching resistance and appropriate electrical resistivity may also beused.

Example metal foams may be of the type formed by pyrolysis and/ormetallisation of a polymer foam such as an open cell polyurethane foam.The metal foams may have an open pore volume of about 90% or greater,for example about 95%, and a pore size of about 0.1-2 mm, for examplefrom about 0.2-1 mm, such as about 0.4 mm.

The porosity of the porous structure 24 may be substantially uniform, ormay vary along the length and/or diameter of the cylinder.

The electrical resistance of the porous structure 24 depends on thegeometry and the material type of the porous structure 24. The powerrequirements to obtain the desired humidification capacity (i.e.throughput of water to be vaporised) determine the required voltage.

FIG. 2b shows an alternative example wherein the thermally conductiveand electrically resistive porous structure 25 comprises fibrousmaterial, for example carbon fibres. Similar to the end 27 of the porousstructure 24, an end 29 of the porous structure 25 may extend beyond anopen end of the outer tube 26. The fibres may preferably be bundled ingroups forming tow, twist, knit, braid, felt woven fabric or tapestructures. The fibrous structure having a plurality of apertures, orpores, which allow fluid to pass therethrough. A detail view showing anexample of a braided bundle of fibres 25 is illustrated in FIG. 3b .Examples of fibrous materials include carbon fibres having a carboncontent of greater than 50% and having precursors of Poly AcrylicNitrile (PAN), rayon or pitch. The carbon fibre diameters may be lessthan about 20 microns, for example about 5 to 7 microns.

In the humidifier assemblies of FIGS. 2a and 2b , which are adapted forhumidification of air for a respirator apparatus such as a positiveairway pressure (PAP) device for treatment of sleep disordered breathing(SDB) of capacity approximately 100 L/minute flow capacity, a humidifierwater throughput of approximately 0 to 10 ml/minute, for example 2 to 5ml/minute, or 0 to 3 ml/minute has been found to be appropriate toachieve a relative humidity of about 80% relative humidity (RH) at 28°C. This requires a vaporisation power of up to about 240 W.Alternatively, with different geometries different power outputs may beused, for example power outputs of up to about 50 W, up to about 100 Wor up to about 200 W.

A smaller water throughput capacity, such as about 0.5-2 ml/min, may besufficient for many medical humidification applications.

Dimensions of the porous structure shown in FIG. 2a may range from about1 mm-5 mm diameter, for example about 2 mm, and a length of about 20mm-200 mm, for example about 100 mm. This provides a volume range forthe porous structure of approximately 10 mm³ to 4000 mm³, for example 15mm³ to 500 mm³, such as 314 mm³.

The outer tube 26 surrounding the porous structure 24, 25 closelysurrounds the porous structure 24, 25 so as to contain the water totravel through the porous structure and to ameliorate by-passing of theporous structure. The outer tube 26 may be formed of materials which areelectrically and thermally insulating, are thermally shock resistant,and which have a low specific heat capacity. A ceramic tube such asalumina or fused quartz may be used, or alternatively a polymer such asheat shrink or silicone rubber tubing may be applied to the outersurface of the porous structure 24, 25. In other forms, it may not benecessary to use an outer tube 26, for example the porous structure maybe located in within some other container.

In operation, a controlled flow of water may be provided by a supplymeans (not shown), for example a micro-pump such as a piezo-electricpump, under pressure from a water supply (also not shown) to the waterinlet 30 of the connector fitting 28. The supply means may be configuredto deliver a desired volume of water to the water inlet 30. This flow ofwater passes into and through the pore structure of the porous structure24, 25 of the humidifier whilst electrical current is also passedthrough the electrically resistive material of the porous structure 24,25. The material of the porous structure 24, 25 thus acts as aresistance heater for the water, which is in intimate contact with itspore structure, heating and vaporising the water as it flows from thewater inlet to the vapour outlet 27 of the humidifier. Steam is thusformed, and is expelled from the vapour outlet 27 of the porousstructure 24, 25 and delivered to the respiratory gas flow path. Thevapour outlet 27 may extend past the end of the surrounding outer tube26 and into the air delivery tube to deliver the steam into therespiratory gas flow path being provided to the patient.

In one unillustrated example, the porous structure 24, 25 may be taperedso as to increase in diameter from the water inlet to vapour outlet,e.g. frustro-conical, to compensate for the expansion of the steam asthe water is vaporised. In this case, the outer tube 26 will becorrespondingly shaped to conform to the shape of the porous structure24, 25.

With comparatively low pressure required to propel the water through theporous structure 24, 25 due to the high open area, and controlling thelevel of humidification by controlling the current passing through theporous structure 24, 25, a gravity feed water supply means such as anexternal water bottle or a collapsible bladder may be utilised in placeof the pump. Distilled water may used to prevent clogging of the porousstructure 24, 25.

The humidifier arrangement may thus provide a relatively compact,efficient and readily controllable humidification apparatus having lowthermal mass and thus rapid control response compared with the prior artwater tub humidification arrangements. More rapid and accurate controlof the humidification may be achieved, as thermal lags are reduced.

In certain examples, the humidifier may be controlled such that theamount of water vapour is dependent on or proportional to the air flowrate to the patient. In addition or alternatively, vapour may begenerated during only a portion of the respiratory cycle, for example ina pulsed cycle synchronised with the patient's inhalation so that waterand electrical power requirements are reduced by not humidifying duringexhalation. This in turn may lead to the use for smaller water suppliesor water tubs, and improved electrical power efficiency and/or batterylife for the devices.

FIG. 7 illustrates an alternative example of the present technology. Asshown, the humidifier (or humidifier assembly) 50 includes a generallyporous structure 52 of a thermally conductive and electrically resistiveporous material. The arrangement of the humidifier 50 is generallysimilar to the example shown in FIGS. 2a and 2b , except in thisexample, the porous structure is encased in an outer housing having twoparts 54 a and 54 b (or alternatively, two separate housings 54 a, 54b). A portion of the porous structure 52 is exposed at an open end ofthe housing 54 a, 54 b, being a steam outlet 56 of the humidifier 50. Onthe other end, a connector fitting 58 receives a liquid (e.g., water)from a liquid supply tube 60, and provides the liquid to the sealingtubes 62 via the sealing tube connection spigots 64. Liquid may beprovided using a pump or by gravity feed or other known liquid transportmeans.

The exposed steam outlet end 56 may be the only portion of thehumidifier assembly 50 that is inserted into an air flow tube (notshown). The steam outlet 56 may be inserted and exposed to the airflowat a variety of angles, for example parallel, perpendicular or at anyangle therebetween to the longitudinal axis of the air flow tube. Withthis humidifier assembly arrangement 50, all the water supply andelectrical connection ends are located together at one end, and thesteam outlet 56 is located at the opposite end. This may provide a morecompact design, and may improve ease of assembly and disassembly. Forexample, the humidifier assembly 50 may be disassembled at the sealingtubes 62, and the liquid supply tube 60 may be disconnected to isolatethe heating element portion 80. The heating element portion 80 may be aconsumable item and be disposed and replaced after multiple usages.Alternatively, the heating element portion 80 may be disassembled fromthe humidifier 50 at the electrical connection 70 end, and disposed andreplaced as a consumable item.

Air Heater Coil

FIG. 4 illustrates an example in which the humidifier 112, generallysimilar to the humidifier shown in FIGS. 2a and 2b described above, issupported within an air delivery tube (or air delivery conduit) 116 of arespiratory apparatus such as a PAP device, or may be supported within aportion of the air delivery tube 116. Reference numbers beginning with a“1” designate similar features as those in FIGS. 2a and 2b (e.g.reference number 128 designates a connector fitting).

When heating air in an air path, it may be desirable to have an airheater having a small volume. This could provide a smaller CPAP device,lower costs and reduce power consumption (e.g., longer battery life forportable devices). An air heater may be used with or without ahumidifier within a respiratory system.

For a given air conduit, its cross section would likely be uniform alongthe longitudinal length (e.g. generally round), so its length woulddetermine the volume. To heat air efficiently, the flow of eachairstream should come in contact with (or be very close to) the heatingwire for effective heat transfer. If the flow is laminar, it may bedesirable for the total cross section of the air path to be “covered”with an axial projection of the heater wires and to have no (or minimal)overlapping wire projections.

A porcupine heater coil may be made on a mandrel by wrapping the wireunder tension around said mandrel. If the mandrel has a circular crosssection, the resulting form would be a helical spring as shown in FIG.8.

If the mandrel has a high aspect ratio rectangular cross section, thenthe resulting form would be a series of star shaped wire bends as shownin FIG. 9. A porcupine coil is wound around a mandrel and when finishedis allowed to spring off the mandrel to take the shape of the coil withstaggered “star” shaped elements having points or corners on the outerperiphery. However, this may result in a large open space along thecentre of the coil where no air heating will occur. The length ofheating wire in the porcupine coil is concentrated around the centralhole area and only the corners or points are on the outer diameter (whenlooking at the end view).

Each of these shapes has a core in the centre which does not heat theair stream flowing through the centre core. To evenly heat the airstream, it would require heat diffusion from the outer hot air to thecooler central air stream. Alternatively, turbulence may be induced tomix the airstream to obtain a uniform air temperature. However, inducingturbulence may increase the impedance of the air flow and increase thepower required for the system.

Another issue with a porcupine coil is that the projected wires may beconcentrated in a fairly narrow annular band (depending on wire tensionand mandrel shape when winding), and the air streams flowing throughthis narrow annular band would generally receive most of the heating.This may cause uneven air heating and may result in furtherinefficiency.

A wire bender may be used to bend the wire into a structure thatachieves a heating area covering an entire or substantially all or mostof the cross section of an air tube, so that air heating may becompleted in a shorter length. A coil may be formed so that the loops ofwire (that go around the centre open core area, as in a porcupinemandrel formed coil) are instead bent as they approach the centre core.A combination of a number of coil loops may thus form the periphery ofthe centre core. This allows the centre core dimensions to be variable,or may be formed such that the centre core closes up completely, thatis, effectively filling the complete or substantially all or most of thecross section with the heating wire.

By choosing the angle of each wire loop around each 360° turn to not bea factor of 360, the subsequent coils would not align with the first“row”. This would allow coverage of a different portion of the crosssectional area by presenting more heating wire to the air steam. Theradius of curvature of the outer bend portion and the inner bend portionmay be used to determine the size of the centre core open cavity. Forexample, determine the shape of the coil by the outer radius, the outerlength of the outer radius, the inner radius and the inner length of theinner radius, as well as the pitch of the coil. These dimensions mayalso determine the inner centre open core space diameter and the outerdiameter of the whole coil structure.

An example of the dimensions of the coil is shown in FIG. 6d . The coilmay have an outer diameter O.D. of about 20 mm to 30 mm, for exampleabout 25.4 mm. The coil may have an inner diameter I.D. of about 1 mm to5 mm, for example about 3.0 mm. The loops of the coil may have an firstlength of about 15 mm to 25 mm, for example about 19.3 mm, and a secondlength of about 5 mm to 12 mm, for example about 8.85 mm. The firstlength L1 may be formed by bending the wire at a radius R1 of about 15mm to 20 mm, for example about 17.4 mm, and the second length L2 may beformed by bending the wire at a radius R2 of about 1 mm to 5 mm, forexample about 3 mm.

The heat radiated by the coil structure may be determined by theresistivity of the coil structure, the longitudinal length of the coilstructure and the cross sectional diameter of the coil structure.

In an alternative example, the coil radii may vary within the coilstructure so that some of the loops F are flatter and are away from thecentre axis of the coil structure. This configuration may give a moreeven uniform coverage of the air stream as shown in FIG. 6 e.

The humidifier 112, schematically represented in FIG. 4, is supportedwithin the air delivery tube 116 by means of one or more mountingstructures 140 such that the major axis of the humidifier is generallyparallel to the axis of the air delivery tube 116 so as to presentminimal interference to the air flow within the tube. That is, thehumidifier is mounted substantially parallel to the longitudinal axis ofthe air delivery tube. Alternatively, the humidifier may be mounted in adifferent configuration that is not along the longitudinal axis, butwherein the steam outlet is exposed to the air flow.

The mounting structure(s) may comprise a coil structure such as a‘helical coil’ or a ‘porcupine coil’ arrangement, for example asillustrated in FIGS. 8 and 9, or a ‘rosette coil’ arrangement formed ofwire to create a formation which engages with the inner surface of theair delivery conduit 116 and with the outer surface of the humidifier112, to hold the humidifier substantially co-axially within the tube, asillustrated in FIGS. 5 and 6. The “rosette coil” structure may be formedusing a wire bending machine. In this arrangement the mounting structuremay also optionally be used as a resistance heater for heating the airflowing within the air delivery tube 116 prior to receiving the watervapour from the humidifier, so that take-up of the vapour by the gasflow is increased.

Referring to FIGS. 4-6 e, a mounting structure 140 in the form of a“rosette” heating coil is shown. In the rosette heating coil the wiresare not wrapped around a mandrel but are formed on a wire bending toolusing two distinct radii. The form of the rosette coil allows aproportionally larger length of heating wire to be located at theperiphery of the coil to heat the larger volume of air that flows inthis region. This form also allows a relatively small hole down thecentre of the coil (and may be adjusted in size) and may be used tosupport the outer tube 26 that encloses the steaming element.

The “petals” or loops of the rosette are designed so that there are amultiple of them on each section or “flower” and the next flower has thepetals offset or overlapping to the previous one so the air path alongthe tube is ensured of being in close proximity to any part of theheating wires at some stage of its flow. The appropriate offset may bechosen so that there is complete coverage of the cross section of theannular area between the outer tube 126 and the air delivery conduit116. The design produces a more compact air heating coil than prior artheating coils.

Humidification and Water Management

The controller 18 (as shown in FIG. 1) may receive signal/s from the atleast one sensor 20 a, 20 b, 20 c and be configured to control thehumidifier to provide the humidified flow of breathable gas at apredetermined temperature and a predetermined relative humidity.Further, the controller 18 may be configured to control the supply ofpower such that vapour is delivered during a portion of a phase of apatient's breathing cycle, for example only during the patient'sinspiratory phase. By doing this, water usage may be managed asrequired, and water conserved to reduce wastage.

The operation of the humidifier may be arranged such that, from knownambient conditions, a desired condition at the patient interface end maybe obtained. For example, first measure the ambient temperature andrelative humidity (or measure temperature and relative humidity at anyidentical point prior to the humidifier, for example within the flowgenerator). Using these measurements, calculate the absolute humidity bythe below formula.

$\begin{matrix}{{P_{ws} = {{A \cdot 10^{(\frac{m \times T}{T + T_{n}})}}\mspace{14mu}({hPa})}},{where}} & (6)\end{matrix}$

Temperature range (° C.) over water: A m Tn max error −20 . . . 506.1162 7.5892 240.71 0.09%  50 . . . 100 5.9987 7.3313 229.1  0.01% A,m, T_(n) = constants see table 1 T = temperature (° C.)

TABLE 1 Item Definition % RH % Relative humidity A, AH Absolute humidityP_(ws) Saturated partial pressure of water vapour over water TTemperature P_(w) Partial pressure of water vapour over water F Air flowrate in liters per minute Q Water volume in milliliters hPa hectapascalK Kelvin degrees C. Celsius degrees Td Dew point temperature (not usedin these calculations)

Then calculate the water vapour pressure from % RH:Calculate P _(w) =P _(ws) *RH/100 (in hPa!)Example:The ambient temperature is 40° C. and the RH is 50%. Calculate T_(d):P _(w) =P _(ws)(40° C.)*50/100=36.88 hPaExample for 30° C. and 80% RH, (Target Point)Pws=6.1162×10*(7.5892×30/(30+240.71))Pws=42.415 hPaandPw=Pws×RH/100Pw=33.932 hPa

Absolute humidity is defined as the mass of water vapour in a certainvolume. If ideal gas behaviour is assumed the absolute humidity can becalculated using (17):A=C*P _(w) /T (g/m³), where  (17)

C=constant 2.16679 gK/J

P_(w)=vapour pressure in Pa

T=temperature i K

Example:

The ambient temperature is 20° C. and the relative humidity is 80%.Calculate absolute humidity:Pw=P _(ws)(20° C.)*80/100=18.7 hPaA=2.16679*1870/(273.16+20)=13.82 g/m³Example for 30° C. and 80% RH, (Target Point)Pw=33.932 hPa (from above)AndAH=2.16679×33912/(273.16+30)AH=24.252 g/m3 (or mg/L)Therefore the Target AH is 24.252 mg/LFor a given flow rate F (in L/min), the quantity of water (Q) to beinjected into the airstream is:Q=(24.252−AH at ambient)×F mg/minFor water near room temperature, 1 mg ˜1 mL.

The desired patient condition may be an absolute humidity of about 24.5mg/L (water/Litre of air). Subtract the measured absolute humidity fromthe 24.5 mg/L and this is the quantity of water that needs to be addedin mg/L. Measure the air flow and multiply the airflow (in L/min) by therequired quantity of water to be added (in mg/L), and the result is thedesired water pumping rate (in mg/min). This quantity of water may bepumped by the piezo-pump which may be controllable by voltage and/orfrequency.

From the water flow rate, the power required may be determined byreference to a chart (FIG. 12) derived empirically.

Modes of Operation

Humidifier Controls

FIG. 10 shows a flow chart of an example mode of humidifier operation.Process steps 1002 show the control of a heated tubing 300. The heatedtubing may be similar to that described in, for example, U.S.2008/0105257 A1 and/or U.S. 2011/0023874 A1, the entire contents of bothbeing incorporated herein by reference. The process begins at SI andincludes receiving measurements of sensed gas temperature delivered tothe patient interface. The sensed gas temperature may be provided from asensor 20 b. A predetermined temperature Tm of gas to be delivered tothe patient interface is provided at S2. The predetermined temperatureTm may be, for example, selected by a user (e.g. clinician) or patientfrom an input of an apparatus as shown in, for example, FIGS. 1a to 1c .The predetermined temperature may also be provided as disclosed in, forexample, U.S. 2009/0223514 A1 and/or U.S. 2011/0023874 A1. The sensor 20b measures a sensed gas temperature and compares with a desired (i.e.predetermined) target temperature provided at S2. The difference ΔTm isdetermined at S6 and is fed back to the controller 18 to control theoperation of the heated tubing 300. This process may be similar to thatdisclosed in U.S. 2009/0223514 A1, the entire contents of which areincorporated herein by reference.

Process steps 1004 determines the required water flow rate to deliver adesired or predetermined target humidity at a desired targettemperature. As previously described in the example calculations, theambient absolute humidity may be calculated by measuring the ambient airtemperature and ambient relative humidity. This ambient absolutehumidity is compared with the target required absolute humidity(calculated using the target (e.g. desired or predetermined) temperatureand relative humidity) to calculate the quantity of water required. Fora sensed gas flow, and knowing the quantity of water that need to bedelivered per unit volume of gas, the water flow rate may be calculated.As shown in FIG. 10, the predetermined delivered gas temperature Tm isprovided at S2 and a predetermined relative humidity RHm to be deliveredto the patient interface is provided at S4. The predetermined relativehumidity RHm may be, for example, selected by the user or patient in amanner similar to that described in, for example, U.S. 2009/0223514 A1and/or U.S. 2011/0023874 A1. The predetermined values of RHm and Tm areprovided to a psychrometric calculation at S8 and the predeterminedabsolute humidity AHm to be delivered to the patient interface isprovided at S12.

The ambient absolute humidity is determined by inputting an ambienttemperature Ta, determined for example by a sensor 20 a, and an ambientrelative humidity RHa, determined for example by a sensor 20 d, into apsychrometric calculation at S10 and providing the ambient absolutehumidity AHa at S14. The difference LAH between the predeterminedabsolute humidity AHm and the ambient absolute humidity Aha isdetermined at S16.

Process steps 1006 show the controls of the power input to both pump thewater and heat the heating element. Using the calculated water flowrate, and knowing a predetermined energy required to adequately pump,heat and vaporise the water, we can determine the voltage, frequency,power etc required for controlling the process of the steam injector.The sensed gas flow F, determined for example by a sensor 20 c, and thedifference DAH are used at S22 to calculate the required water flow rateto deliver the predetermined humidity at the predetermined temperature.Alternatively the flow rate may be estimated based on the motor currentas described in US 2010/0319697. The predetermined voltage and frequencyto pump any predetermined water flow rate is determined or provided atS24 and at S26 the required voltage and frequency to pump the requiredwater flow rate is determined. The predetermined power to vaporise anyliquid flow at S20 is used along with the required pump voltage andfrequency to determine at S28 the required power to vaporise the pumpedliquid flow. The required power determined at S28 is provided to thehumidifier, e.g. to the controller 18.

Process steps 1008 show the controls of the air heater coils of themounting structure 140. By sensing the temperature at the humidifieroutlet, with for example a sensor 20 e, and comparing with the desiredtarget air flow temperature Tm, the difference ΔT between the sensedtemperature provided by the sensor 20 e and the predeterminedtemperature Tm can be determined at S18. The difference ΔT can beprovided to the controller 18 to provide feedback control of the airheater of the mounting structure 140.

It should be appreciated that the controller 18 may be provided tocontrol the liquid transport (e.g. the pump), the air heater (e.g. thecoil of the mounting structure 140), the heated tubing 300, thehumidifier (e.g. the humidifier 112). It should also be appreciated thatthe controller 18 may be a plurality of controllers and that theplurality of controllers may be provided in the various components. Forexample, a controller may be provided in the flow generator, thehumidifier, the pump, the heated tubing, etc. It should also beappreciated that the controller, or each controller, may be in the formof, for example, a microcontroller or a specially programmed generalpurpose computer, or an ASIC. It should further be appreciated that theprocess shown in FIG. 10 may be executed from a software program orother executable code or instructions stored in a memory provided in thecontroller. It should be even further appreciated that the memory(ies)of the controller(s) may include, for example, empirically determinedcoefficients and/or look up tables for use in various psychometric andother calculations of the process.

FIG. 11 shows a flow chart of another example mode of humidifieroperation. FIG. 11 includes all the process steps shown in FIG. 10 andfurther includes control steps 1010 for controlling the operation of theheating element. As shown in 1010, the operation of the heating elementmay be controlled by predetermining a desired target heating elementoutlet temperature at S30. For example, this predetermined temperaturemay be a minimum temperature that is required to fully vaporise theliquid flowing through the heating element. By monitoring the sensedtemperature at the heating element outlet with, for example a sensor 20f, the heating element can be controlled to ensure the minimumtemperature is maintained by determining a difference ΔT at S32 andusing a feedback control loop. It should be noted that in some forms ofthe present technology, not all the steps shown in FIG. 10 or 11 may berequired. In some cases, alternative steps may be included, and othersteps may be omitted.

Balanced Circuit Test

A balanced circuit test may be used to detect if there is a fault withthe air heater and/or the heating element. The balanced circuit test maybe enabled by providing a connection to the center of the heatingelement, in addition to the two electrical connection points provided ateach end of the heating element. Measuring a voltage, current orresistance etc from the center tap to each of the end electricalconnection points, the result of each segment should be the same(balanced) as the other. If the measurements do not match, it mayindicate a fault of the circuit.

Temperature Plausibility Mode

By comparing the sensed temperature at different sensors when theheating element and/or air heater is not turned on, the system may beenabled to detect faults in a sensor that does not provide the sameresult as the other sensors under conditions, when they should providethe same result.

Configuration of Water Supply and Heaters

The liquid supply may be a water bottle that is connected to the pumpinlet such that water may be supplied to the pump and be pumped to theinlet of the heating element. The bottle may be rigid or collapsible. Atthe outlet of the heating element, the water becomes converted to steamand the generated steam is injected into a pressurised air stream. Toimprove the pump operation, the water supply may be pressurised. Thismay balance the system, so the pump does not operate against thepressure experienced at the heating element outlet. An exampleconfiguration is fitting a rigid liquid container with an opening to thetop of the bottle which is connected to the pressurised air stream.Alternatively, a collapsible container may be provided within a rigidhousing which is pressurised. The container may also be allowed toslightly inflate/deflate with a varying pressure. Such a configurationmay allow the use of a zero-head pump for water.

In another alternative, a patient's expiration may be directed toactuate a pumping of the water into the heating element. For example,using a pressure dampening mechanism and controls, the expiratorypressure force from a patient may be applied to pump the water supplywhen the patient's inhalation cycle is occurring. This may assist thepump or replace the functions performed by the pump.

A number of humidifier system configurations may be provided toimplement the present technology. For example, the water supply may belocated near or within the flow generator/humidifier system; or externalto the system and connected to the humidifier via a conduit. The pumpmay be provided near or within the flow generator/humidifier system; orexternal to the system as described above with the water supply; orprovided near the patient interface (mask) and connected to the watersupply and heating elements via conduits. The air heater may be providednear or within the flow generator/humidifier system; near or within theairflow tubing, at a location near the flow generator/humidifier system;at a location along the length of the airflow tubing; or near thepatient interface. The heating element may be provided near or withinthe flow generator/humidifier system; near or within the airflow tubing,at a location near the flow generator/humidifier system; at a locationalong the length of the airflow tubing; or near the patient interface.It is preferable to locate the heating element downstream of the airheater, so that the air heater heating the air flow may help maintainthe water holding capacity of the air flow and maintain the relativehumidity.

Sensors

Temperature sensors may be added to the inlet end and outlet end of thehumidifier to detect fault conditions, for example for use in preventingthe heater element from overheating (e.g. from lack of water). Theconditions detected by the sensors may be indicative of faultconditions.

For example, if the outlet sensor detects a temperature of less than 100C, it may be an indication that steam is not being formed and water maybe coming out instead of steam. This condition may be the result of aheating element failure, incorrect water flow rate, and/or incorrectpower level. If the outlet sensor detects a temperature that issignificantly greater than 100 C, it may be an indication that water mayhave stopped flowing. This may be the result of a pump failure and/orblockage.

If the inlet sensor detects a temperature that is near room temperatureand power is applied, it may be an indication that water is flowing(i.e. the heating element is not dry heating). If the inlet sensordetects a temperature that is significantly greater than roomtemperature, it may be an indication that water is not flowing, or toomuch power is being applied.

The sensors generally have an expected operating range during normaloperation, so any deviation from the expected operating condition mayindicate sensor failure. The sensors may also be used to control thepower to the heating element instead of using an empirical chart such asChart 1.

An air temperature sensor may be located downstream of the air heaterand steam injection outlet location. This sensor may detect the realtime air temperature and be in close loop feedback to control the powerapplied to the air heater coil structure. Accordingly, the humidifiedair temperature may be controlled and adjusted to the desired condition,for example 30C.

Sterilisation & Cleaning Modes

The humidifier may utilise dry heat sterilisation to destroymicro-organisms. That is, heating the humidifier in the absence of watervapour for a period of time, such that micro-organisms are destroyed bythe heating process. Dry heat sterilisation for a CPAP humidifier may beactivated for example during day time, when the patient is not using thedevice. Alternatively, it may run before and/or after a patient'stherapy session.

Some example heating temperature-time processes that may be effectivefor dry heat sterilisation are:

-   -   160-170 degrees C. for 120 minutes;    -   170-180 degrees C. for 60 minutes; and    -   180-190 degrees C. for 30 minutes.        Heating at a higher temperature for a shorter period of time, or        lower temperature for a longer period of time, may also be        effective.

As previously described, the humidifier may have temperature sensorslocated at the inlet and outlet ends of the heating element. Thetemperature levels detected by the sensors may be input into a closeloop feedback system, to control the heating element to heat to desiredtemperature levels for a chosen time period. Alternatively, or incombination with the heating element, the air heater coil may also beheated for the dry heat sterilisation process.

The humidifier may have wet heating/unheated cleaning functional modesfor removing residues, deposits and/or micro-organisms from the heatingelement. The humidifier may be configured to allow a liquid flow throughthe heating element (with or without activation of heating elementresistance heating) to flush out any unwanted particles or organisms.The cleaning mode may be initiated for example before and/or after apatient's therapy session. The cleaning mode may be set up by varyingcontrol parameters of liquid flow rate, heating temperature, and runcontinuously or in varying frequency periods. The timing of theactivation/deactivation of the cleaning mode may be monitored and/orcontrolled using a timer.

One advantage of certain aspects of the present technology is that asmaller and/or more compact humidifier may be provided. For example, thevolume of water may be reduced. Another aspect of certain forms of thepresent technology is that the forms may be cheaper, for example wherethe water is in a separate system and not pressurised, then certainpressure seals may not be required within the tub. In certain forms,there may be less of a need for spillback protection since less water ispresent.

An advantage of certain aspects of the present technology is that ahumidifier may be provided that can respond more rapidly to changingcircumstances, for example on a breath by breath basis, or to lead to amore rapid start up. An advantage of certain aspects of the presenttechnology is to provide more precise control over the amount ofhumidification provided.

Another advantage of certain aspects of the present technology is a moreefficient energy use, through the use of a more efficient heatingelement. Another advantage of certain aspects of the present technologyis that they enable a wide range of different shapes and/orconfigurations to be manufactured, for example, a heating element thatmay be arranged in a variety of different shapes and/or configurations.In one form a heating element may be provided within the humidificationtube.

While particular embodiments of this technology have been described, itwill be evident to those skilled in the art that the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. The present embodiments and examplesare therefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than the foregoing description, and all changes which comewithin the meaning and range of equivalency of the claims are thereforeintended to be embraced therein. It will further be understood that anyreference herein to known prior art does not, unless the contraryindication appears, constitute an admission that such prior art iscommonly known by those skilled in the art to which the inventionrelates.

The invention clamed is:
 1. A humidifier for increasing a humidity of asupply of air, the humidifier comprising: an enclosed gas flow path forthe supply of air; a heating element including a porous structure ofelectrically resistive and thermally conductive material configured tosubstantially vaporise liquid that is passed through the porousstructure, the porous structure having a liquid inlet and a vapouroutlet; and an outer housing surrounding at least a portion of theporous structure for containing the liquid and vapour within the porousstructure, an enclosure of the enclosed gas flow path surrounding theouter housing so that the enclosed gas flow path is between the outerhousing and the enclosure of the enclosed gas flow path and the heatingelement and the outer housing are immersed within the supply of air inthe enclosed gas flow path; wherein the porous structure includes afirst electrical connector and a second electrical connector, the firstelectrical connector and the second electrical connector beingconfigured for receiving electrical power and applying a voltage acrossthe porous structure so that the porous structure generates heat; andthe vapour outlet is arranged to expel heated vapour for delivery intothe enclosed gas flow path to increase the humidity of the supply ofair.
 2. The humidifier according to claim 1, wherein the firstelectrical connector is located at or near the liquid inlet and thesecond electrical connector is located at or near the vapour outlet. 3.The humidifier according to claim 1, further comprising a connectorfitting configured to deliver liquid from a supply of liquid to theliquid inlet.
 4. The humidifier according to claim 3, wherein theconnector fitting comprises a connection spigot, and the humidifierfurther comprises a sealing tube configured to form a sealed connectionbetween the connection spigot and the outer housing.
 5. The humidifieraccording to claim 3, wherein the connector fitting comprises a liquidinlet spigot configured to receive liquid from the supply of liquid, andwherein the humidifier further comprises a liquid supply tube connectedto the liquid inlet spigot.
 6. The humidifier according to claim 1,wherein the porous structure and the outer housing are each elongate,and the vapour outlet of the porous structure extends beyond the outerhousing and is configured to be exposed to a flow of breathable gas tobe humidified through an open end of the outer housing.
 7. Thehumidifier according to claim 1, wherein the porous structure has acylindrical shape or a tapered shape.
 8. The humidifier according toclaim 1, wherein the porous structure is formed of an open pore metalfoam and the open pore metal foam comprises a chromium alloy, thechromium alloy comprising MCrAlX, where M is one or more of Nickel (Ni),Cobalt (Co) or Iron (Fe) contributing at least 50% by weight, Chromium(Cr) contributing between 8% and 35% by weight, Aluminium (Al)contributing greater than 0% but less than 8% by weight, and Xcontributing less than 25% by weight, with X including zero or moreother elements, including Molybdenum (Mo), Rhenium (Re), Ruthenium (Ru),Titanium (Ti), Tantalum (Ta), Vanadium (V), Tungsten (W), Niobium (Nb),Zirconium (Zr), Boron (B), Carbon (C), Silicon (Si), Yttrium (Y) andHafnium (Hf).
 9. The humidifier according to claim 8, wherein the openpore metal foam is formed by pyrolysis and/or metallisation of a polymerfoam.
 10. The humidifier according to claim 1, wherein the porousstructure comprises a body of carbon fibres bundled in a form of tow-,twist-, knit-, braid-, felt-, woven fabric- or tape- structures, thebody of carbon fibres having precursors of Poly Acyrlic Nitrile, rayonand/or pitch.
 11. The humidifier according to claim 1, wherein theporous structure is formed of ceramic material.
 12. The humidifieraccording to claim 1, wherein the porous structure has a substantiallyuniform porosity or has a porosity that varies along its length and/ordiameter.
 13. The humidifier according to claim 1, wherein the outerhousing is formed of electrically and thermally insulating material. 14.The humidifier according to claim 13, wherein the outer housing isformed of alumina, fused quartz, or a polymer.
 15. The humidifieraccording to claim 1, wherein the humidifier is adapted for mountingwithin an air delivery tube, and further comprises a mounting structurefor mounting the humidifier within the air delivery tube, the mountingstructure being adapted to space the humidifier from an internal wall ofthe air delivery tube.
 16. The humidifier according to claim 15, whereinthe mounting structure includes a coil structure adapted to mount thehumidifier substantially parallel to a longitudinal axis of the airdelivery tube, the coil structure comprising a resistance heaterconfigured to heat air flowing through the air delivery tube.
 17. Thehumidifier according to claim 1, further comprising a power supplyconfigured to supply the voltage across the porous structure, and acontroller configured to control the power supply such that vapour isdelivered only during a portion of a phase of a patient's breathingcycle.
 18. The humidifier according to claim 1, wherein the heatingelement is configured so that the liquid flowing through the porousstructure is heated predominantly by the heat generated by the porousstructure.
 19. The humidifier according to claim 1, wherein the heatingelement is oriented so that the liquid passes through the porousstructure in a direction substantially parallel to the flow of airthrough the gas flow path.
 20. The humidifier according to claim 1,wherein the heating element and the outer housing are arranged so thatthe liquid is centrally dispersed into the heating element and the vaporis outwardly dispersed into the gas flow path.
 21. A respiratoryapparatus for delivering a flow of breathable gas to a patient,comprising: a flow generator configured to generate the flow ofbreathable gas; a liquid supply; and the humidifier according to claim 1configured to receive a volume of liquid from the liquid supply,vapourize the volume of liquid and deliver the vapour into the flow ofbreathable gas to create a humidified flow of breathable gas.
 22. Therespiratory apparatus according to claim 21, wherein the liquid supplycomprises a micro-pump or a piezo-electric pump.
 23. A respiratorydevice configured to deliver breathable gas to a patient, therespiratory device comprising: an air delivery tube with a longitudinalaxis; and an air heater coil adapted to heat an airflow within the airdelivery tube, the air heater coil comprising a plurality of loops orpetals, each loop or petal arranged to overlap an adjacent loop or petalin a direction along the air delivery tube longitudinal axis to form arosette configuration adapted to cover substantially all or most of across-sectional area of an air flow path within the air delivery tube.24. The respiratory device according to claim 23 further comprising: aflow generator configured to pressurize a flow of breathable gas, theflow generator being in pneumatic communication with the air deliverytube; a humidifier configured to humidify the pressurized breathablegas; and a patient interface connected to the air delivery tube.
 25. Therespiratory device according to claim 23, wherein the plurality of loopsor petals are formed of resistive wire.
 26. The respiratory device ofclaim 23, wherein at least some of the plurality of loops or petalsextend radially from the air delivery tube longitudinal axis.